The present invention relates to methods for determining a position of a rotating shaft.
Crankshaft position information and/or camshaft position information is vital to provide accurate spark plug ignition and fuel injection in most vehicle engines. One prior art system for detecting the position of a rotating shaft utilizes feature pattern recognition to determine a synchronization or sync position of the shaft. The prior art system includes a target wheel having a predetermined feature pattern rotating with the shaft during engine operation, means for generating an electrical signal in response to rotation of the feature pattern, and means for identifying a sync period from the generated feature pattern signal and determining the sync position of the shaft. The feature pattern is formed with a plurality of timing features including a sync feature. The sync feature can be either an extra or missing timing feature on the target wheel.
FIG. 1 is a graph illustrating an electrical signal 10 produced in response to rotation of a feature pattern on a target wheel fixed to an engine shaft and including a sync period determined in accordance with a prior art method. The feature pattern includes six consecutive timing features producing six consecutive pulses, labeled as 1-6 respectively in FIG. 1, and a seventh or sync feature producing one pulse, labeled as 7 in FIG. 1. In this embodiment, the seventh or sync feature is uniquely spaced on the target wheel. More specifically, consecutive features are equally spaced with the exception of the sync or seventh feature which is uniquely spaced by a shorter distance from the sixth and first timing features. In other words, the fifth and sixth timing features and the sixth and first timing features are equally spaced, and the seventh or sync feature is disposed between the sixth and first timing features with the sync feature spaced closer to the sixth feature than the first feature.
One prior art method of identifying the sync period includes the steps of: measuring time periods between consecutive pulses; determining whether the current time period is a predetermined fraction of the last time period; and if the current time period is a predetermined fraction of the last time period, measuring the next time period and determining if the next time period is a predetermined multiple of the current time period to locate the sync period and determine the sync position of the shaft. For example, assume that the current time period (tc) is the time period between the sixth pulse and the seventh pulse as labeled in FIG. 1. If the current time period (tc) is the predetermined fraction of the last time period (tl), i.e. the time period between the fifth pulse and the sixth pulse as labeled in FIG. 1, then the next time period (tn), i.e. the time period between the seventh pulse and the first pulse as labeled in FIG. 1, is measured. If the next time period (tn) is a predetermined multiple of the current time period (tc), then the sync period is determined to be the time period between the sixth pulse and the seventh pulse.
However, some vehicle engines produce large engine r.p.m. oscillations during starting conditions shortening or lengthening the time period being measured and, thus, resulting in either missed feature recognition or false feature detection of the sync period when using the prior art method. Accordingly, there is a desire to provide an improved method of determining a position of an engine shaft during engine operation or shaft rotation.
The present invention provides a method for determining a position of a rotating shaft and, more particularly, for determining a synchronization or sync position of an engine crankshaft or engine camshaft. The method includes sequentially measuring consecutive time periods generated in response to rotation of the shaft, and comparing each measured time period to a value calculated from a predetermined function based on more than one measured time period to determine the sync position.
Preferably, the comparing step includes the step of comparing a penultimate measured time period to a product of a sync factor and the sum of an ultimate measured time period, the penultimate measured time period, and an antepenultimate measured time period.
After determining the sync position, the method includes sequentially measuring a predetermined number of consecutive time periods generated in response to further or continued rotation of the shaft, and comparing a penultimate measured time period to a value calculated from the predetermined function to verify the sync position. In other words, after the sync position is located, the method performs the comparing step to verify the sync position only with selected time periods or at selected sync and timing features.